Hardness against toughness
Tungsten carbide, zirconia, alumina, SiC: hardness against toughness
Tungsten carbide (WC, cemented carbide with a cobalt binder) measures 1,200 to 1,605 HV30, or 11.8 to 15.7 GPa Vickers, across 6 cobalt-bonded grades (per Hyperion Materials), the same range as alumina (Al2O3), alumina-toughened zirconia (ATZ) and yttria-stabilised zirconia (3Y-TZP), and below titanium diboride (TiB2) at 25 GPa Vickers (per Munro's 2000 NIST review). We hold no fracture toughness for tungsten carbide in any source, so it cannot be placed beside the 20 ceramic and carbide grades that have both values; the toughest of them, Magnesia partially stabilised zirconia (Mg-PSZ), Nilcra Zirconia TS grade, reaches 15 MPa m^0.5 (per Morgan Advanced Materials).
Hardness is resistance to an indenter; fracture toughness (KIc, in MPa m^0.5) is resistance to a crack growing. A Pareto staircase joins the materials that no other material beats on both. The two properties pull against each other, and the staircase shows where.
Why is tungsten carbide called tough when ceramics are harder?
Tungsten carbide is called tough because its cobalt binder trades hardness for toughness, not because a measured toughness puts it above ceramics. Hyperion Materials prints 1,300 to 1,605 HV30 for 6% cobalt grades and 1,200 HV30 for 10% cobalt (12.7 to 15.7 and 11.8 GPa Vickers). No fracture toughness for tungsten carbide is found in any source we hold.
Cemented carbide, also called hardmetal, is tungsten carbide grains held together by a cobalt binder. The tungsten carbide profile says that Hyperion Materials ties high toughness to 10 to 20 percent binder and high hardness to sub-micron grains with 3 to 15 percent binder. That is a trend, and our data holds only the hardness half of it.
- Cobalt-bonded tungsten carbide grade
- Pure WC compound, aggregator site
- Other materials
Data behind this chart (30 records)
Reading it. Each bar is one Vickers record at room temperature, in GPa. Hardness stored in HV30 or kgf/mm² is converted with 1 HV = 9.80665 MPa; HRC, HRA and HB numbers are never converted. The metal itself, tungsten, measures 3.4 GPa Vickers (no test conditions stated), so cobalt-bonded WC is 3.4 to 4.6 times harder than the metal. Inside the WC range: Alumina (Al2O3), Kyocera AO479O at 15.2 GPa; Alumina-toughened zirconia (ATZ), ATZ-20 at 13.8 GPa; Yttria-stabilised zirconia (3Y-TZP), 3Y-TZP reference material from the same paper at 13.8 GPa; Alumina-toughened zirconia (ATZ), ATZ-10 at 13.1 GPa. Above it: Cubic boron nitride (cBN) at 33 to 45 GPa; Titanium diboride (TiB2) at 25 GPa; Silicon carbide (SiC) at 23.9 GPa; Tantalum carbide (TaC) at 22.8 GPa.
| Grade | Cobalt, wt % | WC grain size, as printed | Typical use, as printed | Hardness, HV30 | Hardness, GPa Vickers | Source |
|---|---|---|---|---|---|---|
| H6N | 6 | Normal | Crusher parts | 1,605 | 15.7 | Hyperion Materials |
| PM06 | 6 | Normal | Mining drill bits | 1,440 | 14.1 | Hyperion Materials |
| H6T | 6 | not printed | not printed | 1,350 | 13.2 | Hyperion Materials |
| H6P | 6 | Coarse | Mining drill bits | 1,340 | 13.1 | Hyperion Materials |
| PS06 | 6 | Coarse | Mining drill bits | 1,300 | 12.7 | Hyperion Materials |
| PN10 | 10 | Coarse | HPGR studs | 1,200 | 11.8 | Hyperion Materials |
| pure WC compound (no binder) | 0 | not printed | not printed | 2,600 HV, approximate | 25.5 | WebQC, an aggregator site |
Hardness falls as cobalt rises: 6% cobalt runs 1,300 to 1,605 HV30, 10% cobalt runs 1,200 HV30. Within 6% cobalt the grain size matters too: normal-grain grades (H6N and PM06) run 1,440 to 1,605 HV30 and coarse-grain grades (H6P and PS06) run 1,300 to 1,340 HV30 (grain sizes are printed as words, with no micrometre value). The pure WC row is an approximate figure from WebQC, an aggregator site with no primary reference, so it is not treated as a grade.
Which ceramic gives the best mix of hardness and fracture toughness?
No ceramic wins on both axes. 20 materials hold hardness and fracture toughness from one datasheet; 5 sit on the staircase, from Titanium diboride (TiB2), per Lv et al.'s 2024 review (30 GPa, 4.5 MPa m^0.5) to Magnesia partially stabilised zirconia (Mg-PSZ), Nilcra Zirconia TS grade (10 GPa, 15 MPa m^0.5). The other 15 are beaten on both axes by another material, including Silicon carbide (SiC) at 23.9 GPa and 2.8 MPa m^0.5.
The plot places a material only when its hardness and its fracture toughness come from the same source and grade, so every marker is one real product. A material is dominated when another one is at least as hard and at least as tough and better on one of the two. The staircase joins the ones that are not. Ranges are plotted at their midpoint, with a whisker for the range.
20 materials hold both values from one datasheet. 5 sit on the staircase when every hardness test is counted; 4 when only Vickers is counted.
Swipe the plot sideways to see all of it.
- Vickers
- Knoop
- Test not stated
- Oxide
- Carbide, nitride, boride, silicide
- On the staircase
Materials that meet your floors
| No. | Material and grade | Hardness, GPa (test) | Fracture toughness, MPa m^0.5 | Compressive strength, MPa | Source | Vickers-only view |
|---|---|---|---|---|---|---|
| 1 | Titanium diboride (TiB2), per Lv et al.'s 2024 review | 25 to 35 GPa, midpoint plotted (test not stated) | 4 to 5 MPa m^0.5, midpoint plotted | not found in any source we hold for this grade | Lv et al.'s 2024 review | not counted (test not stated) |
| 4 | Titanium diboride (TiB2), per Munro's 2000 NIST review | 25 GPa (Vickers) | 6.2 MPa m^0.5 | not found in any source we hold for this grade | Munro's 2000 NIST review | on the staircase |
| 10 | Alumina-toughened zirconia (ATZ), ATZ-20 | 13.8 GPa (Vickers) | 10.9 MPa m^0.5 | not found in any source we hold for this grade | an ATZ composites paper | on the staircase |
| 14 | Yttria-stabilised zirconia (YSZ), CoorsTek YTZP | 12.7 GPa (Knoop) | 13 MPa m^0.5 | not found in any source we hold for this grade | CoorsTek | not counted (Knoop) |
| 19 | Magnesia partially stabilised zirconia (Mg-PSZ), Nilcra Zirconia TS grade | 10 GPa (1,020 kg/mm2 as printed) (Vickers) | 15 MPa m^0.5 | 1,800 MPa | Morgan Advanced Materials | on the staircase |
| No. | Material and grade | Hardness, GPa (test) | Fracture toughness, MPa m^0.5 | Beaten on both axes by | Vickers-only view |
|---|---|---|---|---|---|
| 2 | Boron carbide (B4C), Norbide hot pressed | 27.5 GPa (2,800 kg/mm2 as printed) (Knoop) | 3.1 MPa m^0.5 | no. 1, Titanium diboride (TiB2), per Lv et al.'s 2024 review (30 GPa, 4.5 MPa m^0.5) | not counted (Knoop) |
| 3 | Silicon carbide (SiC), UltraSiC | 26 GPa (Knoop) | 3.5 MPa m^0.5 | no. 1, Titanium diboride (TiB2), per Lv et al.'s 2024 review (30 GPa, 4.5 MPa m^0.5) | not counted (Knoop) |
| 5 | Silicon carbide (SiC) | 23.9 GPa (Vickers) | 2.78 to 2.82 MPa m^0.5, midpoint plotted | no. 4, Titanium diboride (TiB2), per Munro's 2000 NIST review (25 GPa, 6.2 MPa m^0.5), and 1 more | beaten by no. 4 |
| 6 | Metal boride NbB2 | 20.3 GPa (test not stated) | 4 MPa m^0.5 | no. 4, Titanium diboride (TiB2), per Munro's 2000 NIST review (25 GPa, 6.2 MPa m^0.5), and 1 more | not counted (test not stated) |
| 7 | Lanthanum hexaboride (LaB6) | 20 GPa (test not stated) | 3.02 MPa m^0.5 | no. 4, Titanium diboride (TiB2), per Munro's 2000 NIST review (25 GPa, 6.2 MPa m^0.5), and 1 more | not counted (test not stated) |
| 8 | Silicon nitride (Si3N4), SN-GP | 14.5 GPa (test not stated) | 6.2 MPa m^0.5 | no. 4, Titanium diboride (TiB2), per Munro's 2000 NIST review (25 GPa, 6.2 MPa m^0.5) | not counted (test not stated) |
| 9 | Zirconia-toughened alumina (ZTA), CoorsTek Zirconia-Toughened Alumina | 14.4 GPa (Knoop) | 5 to 6 MPa m^0.5, midpoint plotted | no. 4, Titanium diboride (TiB2), per Munro's 2000 NIST review (25 GPa, 6.2 MPa m^0.5) | not counted (Knoop) |
| 11 | Yttria-stabilised zirconia (3Y-TZP), 3Y-TZP reference material from the same paper | 13.8 GPa (Vickers) | 5.1 MPa m^0.5 | no. 10, Alumina-toughened zirconia (ATZ), ATZ-20 (13.8 GPa, 10.9 MPa m^0.5), and 1 more | beaten by no. 10 |
| 12 | Alumina-toughened zirconia (ATZ), ATZ-10 | 13.1 GPa (Vickers) | 9.8 MPa m^0.5 | no. 10, Alumina-toughened zirconia (ATZ), ATZ-20 (13.8 GPa, 10.9 MPa m^0.5) | beaten by no. 10 |
| 13 | Yttria-stabilised zirconia (YSZ), Nilcra Zirconia 3Y-TZP Grade | 12.7 GPa (1,300 kg/mm2 as printed) (Vickers) | 10 MPa m^0.5 | no. 10, Alumina-toughened zirconia (ATZ), ATZ-20 (13.8 GPa, 10.9 MPa m^0.5) | beaten by no. 10 |
| 15 | Alumina-toughened zirconia (ATZ), ATZ-B | 12 GPa (Vickers) | 12.7 MPa m^0.5 | no. 14, Yttria-stabilised zirconia (YSZ), CoorsTek YTZP (12.7 GPa, 13 MPa m^0.5) | on the staircase |
| 16 | Magnesia partially stabilised zirconia (Mg-PSZ), Kyocera FZM | 12 GPa (Vickers) | 6.3 MPa m^0.5 | no. 10, Alumina-toughened zirconia (ATZ), ATZ-20 (13.8 GPa, 10.9 MPa m^0.5), and 1 more | beaten by no. 10 |
| 17 | Magnesia partially stabilised zirconia (Mg-PSZ), CoorsTek MgO partially stabilised zirconia column | 11.8 GPa (Knoop) | 11 MPa m^0.5 | no. 14, Yttria-stabilised zirconia (YSZ), CoorsTek YTZP (12.7 GPa, 13 MPa m^0.5) | not counted (Knoop) |
| 18 | Aluminium nitride (AlN), typical commercial AlN | 10.8 GPa (1,100 Kg/mm2 as printed) (test not stated) | 2.6 MPa m^0.5 | no. 10, Alumina-toughened zirconia (ATZ), ATZ-20 (13.8 GPa, 10.9 MPa m^0.5), and 3 more | not counted (test not stated) |
| 20 | Molybdenum disilicide (MoSi2), Kanthal Super 1700 | 9 GPa (Vickers) | 3 to 4 MPa m^0.5, midpoint plotted | no. 10, Alumina-toughened zirconia (ATZ), ATZ-20 (13.8 GPa, 10.9 MPa m^0.5), and 4 more | beaten by no. 10 |
How far to trust it. Hardness is marked Vickers, Knoop or test not stated, and these scales differ for the same material (general engineering knowledge, not in our data), so the Vickers-only view is the cleaner comparison: its staircase has 4 members, no. 4, no. 10, no. 15 and no. 19. Fracture toughness depends on the test too; the records here use notched beam, indentation, SEVNB or an unstated method, and the table of toughness records below shows which. Do not read a gap of a few tenths as a difference.
Silicon carbide (SiC) (23.9 GPa, 2.8 MPa m^0.5, per the NIST Structural Ceramics Database) is beaten by Titanium diboride (TiB2), per Munro's 2000 NIST review (25 GPa, 6.2 MPa m^0.5). Silicon nitride (Si3N4) (14.5 GPa, 6.2 MPa m^0.5, per QSil) is beaten by Titanium diboride (TiB2), per Munro's 2000 NIST review; its compressive strength of 3,000 MPa per the same datasheet is a separate advantage the plot does not show. Tungsten carbide is not on the plot at all, because it has no toughness to place; it appears on the rail under the x-axis.
Which materials have only one of the two values, and why are they not plotted?
35 profiles hold hardness or fracture toughness without a partner from the same datasheet and grade, and 4 hold both from different products. They are parked in the incomplete tray below, not guessed. Tungsten carbide is in the first group: hardness for 6 cobalt-bonded grades, no toughness.
Hardness held, fracture toughness not found in any source we hold 30
These materials cannot be placed on the staircase. Where a hardness is shown in GPa it is on the hardness rail under the plot.
| Material | Hardness records as printed | Fracture toughness records as printed | Why it is parked |
|---|---|---|---|
| 1.2316 stainless plastic mould steel (EN 1.2316, printed name X38CrMo16) | 30 to 48 HRC (Rockwell C; 1 record); 230 to 325 HB (Brinell; 3 records) | not found in any source we hold | no fracture toughness record in any source we hold |
| 1.2738 plastic mould steel (40CrMnNiMo8-6-4, AISI P20+Ni) | 235 to 330 HB (Brinell; 6 records); 28 to 51 HRC (Rockwell C; 7 records) | not found in any source we hold | no fracture toughness record in any source we hold |
| AISI A2 air-hardening cold-work tool steel (EN 1.2363, X100CrMoV5) | 241 HB (Brinell; 1 record); 59 to 61 HRC (Rockwell C; 3 records) | not found in any source we hold | no fracture toughness record in any source we hold |
| AISI D2 cold-work tool steel (EN 1.2379, X153CrMoV12) | 35 to 65 HRC (Rockwell C; 13 records); 210 to 255 HB (Brinell; 2 records); 950 to 1,250 HV1 = 9.3 to 12.3 GPa (Vickers; 2 records) [coating or film records included] | not found in any source we hold | no fracture toughness record in any source we hold |
| AISI H13 hot-work tool steel (EN 1.2344, X40CrMoV5-1) | 45 to 54 HRC (Rockwell C; 6 records); 180 to 229 HB (Brinell; 2 records); 900 to 1,100 HV0.2 = 8.8 to 10.8 GPa (Vickers; 2 records) [coating or film records included] | not found in any source we hold | no fracture toughness record in any source we hold |
| Barium titanate | 4.5 - (Mohs; 1 record) | not found in any source we hold | no fracture toughness record in any source we hold |
| Chromium carbide (Cr3C2) | 2,280 kg/mm2 = 22.4 GPa (Vickers; 1 record); 18.2 GPa (test not stated; 1 record); 15.1 to 18.9 GPa (Vickers; 1 record) [calculated values included] | not found in any source we hold | no fracture toughness record in any source we hold |
| Chromium diboride | 9.72 to 12.46 GPa (nanoindentation; 2 records); 7.97 to 10.09 GPa (test not stated; 2 records) [coating or film records included] | not found in any source we hold | no fracture toughness record in any source we hold |
| Chromium nitride | 1,800 to 2,100 HV = 17.7 to 20.6 GPa (Vickers; 2 records); 22 GPa (test not stated (Knoop or Vickers); 1 record) [coating or film records included] | not found in any source we hold | no fracture toughness record in any source we hold |
| Chromium oxide thermal spray coating (Cr2O3, chromia) | 900 to 1,200 HV300 = 8.8 to 11.8 GPa (Vickers; 1 record); 62 to 72 HRC (Rockwell C; 1 record); 1,496 to 1,762 HV300 g (Vickers; 2 records) [coating or film records included] | not found in any source we hold | no fracture toughness record in any source we hold |
| Cubic boron nitride | 33 to 45 GPa (Vickers; 1 record); 3,000 to 3,200 kg/mm2 = 29.4 to 31.4 GPa (Vickers; 1 record) [coating or film records included] | not found in any source we hold | no fracture toughness record in any source we hold |
| CVD diamond (polycrystalline and single-crystal) | 70 to 120 GPa (test not stated; 2 records) | not found in any source we hold | no fracture toughness record in any source we hold |
| Hafnium carbide | 32.95 GPa (Vickers; 1 record) [calculated values included] | not found in any source we hold | no fracture toughness record in any source we hold |
| Lanthanum hexaboride | 87.5 RA (Rockwell A; 1 record) | not found in any source we hold | other records of this material that have no partner from the same datasheet and grade |
| Magnesium oxide (magnesia) | 692 Knoop (Knoop (number printed with no unit); 1 record); 5 Mohs (Mohs; 1 record) | not found in any source we hold | no fracture toughness record in any source we hold |
| MAX phase ceramics | 4 to 6 GPa (Vickers; 3 records) | not found in any source we hold | no fracture toughness record in any source we hold |
| Metal borides (transition-metal diborides and boride layers) | 16 to 23 GPa (test not stated; 3 records); 38.3 GPa (Vickers; 1 record) [calculated values included, coating or film records included] | not found in any source we hold | other records of this material that have no partner from the same datasheet and grade |
| P20 plastic mould steel (AISI P20, UNS T51620, EN 1.2311) | 230 to 325 HB (Brinell; 4 records); 28 to 51 HRC (Rockwell C; 8 records) | not found in any source we hold | no fracture toughness record in any source we hold |
| Silver steel (BS 1407 high-carbon bright tool steel) | 207 to 285 HB (Brinell; 2 records); 51 to 66 HRC (Rockwell C; 4 records); 65 to 68 Rc (Rockwell C; 1 record) | not found in any source we hold | no fracture toughness record in any source we hold |
| Steatite | 5.8 GPa (Vickers; 1 record) | not found in any source we hold | no fracture toughness record in any source we hold |
| Strontium titanate | 6 to 6.5 - (Mohs; 1 record) | not found in any source we hold | no fracture toughness record in any source we hold |
| Tantalum carbide | 1,790 kg/mm2 = 17.6 GPa (test not stated; 1 record); 22.8 GPa (Vickers; 1 record) [coating or film records included] | not found in any source we hold | no fracture toughness record in any source we hold |
| Titanium diboride | 4.6 to 11 GPa (Vickers; 2 records) [some at high temperature] | not found in any source we hold | other records of this material that have no partner from the same datasheet and grade |
| Titanium nitride | 20 GPa (test not stated; 1 record); 23.39 GPa (Vickers; 1 record) [calculated values included, coating or film records included] | not found in any source we hold | no fracture toughness record in any source we hold |
| Tungsten | 3,430 MN m-2 = 3.4 GPa (Vickers; 1 record); 2,570 MN m-2 (Brinell; 1 record); 7.5 (no units) (Mohs; 1 record) | not found in any source we hold | no fracture toughness record in any source we hold |
| Tungsten carbide (cemented carbide) | 1,200 to 1,605 HV30 = 11.8 to 15.7 GPa (Vickers; 6 records); 90 HRA (Rockwell A; 1 record); 2,600 HV = 25.5 GPa (Vickers; 1 record) | not found in any source we hold | no fracture toughness record in any source we hold |
| Vanadium carbide | 8 to 9 Mohs (Mohs; 1 record); 2,400 HV = 23.5 GPa (Vickers; 1 record) [coating or film records included] | not found in any source we hold | no fracture toughness record in any source we hold |
| Vanadium nitride | 13 GPa (test not stated; 1 record); 20.3 GPa (Vickers; 1 record) [calculated values included] | not found in any source we hold | no fracture toughness record in any source we hold |
| Zirconium carbide | 31.3 GPa (test not stated; 1 record); 25.2 GPa (nanoindentation; 1 record) | not found in any source we hold | no fracture toughness record in any source we hold |
| Zirconium nitride | 23 to 39.3 GPa (nanoindentation; 2 records) [coating or film records included] | not found in any source we hold | no fracture toughness record in any source we hold |
Fracture toughness held, or extra records with no partner from the same datasheet and grade 5
A toughness with no hardness from the same datasheet is not joined to a hardness from another one.
| Material | Hardness records as printed | Fracture toughness records as printed | Why it is parked |
|---|---|---|---|
| Aluminium nitride | not found in any source we hold | 3.03 to 3.25 MPa m 1/2 (K_IC as labelled in the CoorsTek table; test method not stated; 2 records) | other records of this material that have no partner from the same datasheet and grade |
| Boron carbide | not found in any source we hold | 3 to 4 MPa m 1/2 (test method not stated; 1 record) | other records of this material that have no partner from the same datasheet and grade |
| Magnesia-stabilised zirconia and other zirconia grades | not found in any source we hold | 3.5 MPa√m (IF method, as printed; 1 record) | other records of this material that have no partner from the same datasheet and grade |
| Silicon carbide | not found in any source we hold | 4 MPa·m1/2 (test method not stated; 1 record) | other records of this material that have no partner from the same datasheet and grade |
| Silicon nitride | not found in any source we hold | 1.65 to 6.35 MPa m1/2 (Surface crack in flexure test; unevaluated in the NIST record, test method not stated; 5 records) | other records of this material that have no partner from the same datasheet and grade |
Both held, but from different products or datasheets 4
The two values belong to different grades or sources of the same material, so they are listed side by side and not joined.
| Material | Hardness records as printed | Fracture toughness records as printed | Why it is parked |
|---|---|---|---|
| Alumina | 15.2 GPa (Vickers; 1 record) | 4 to 5 MPa·√m (notched beam; 1 record) | both properties held, but from different products or datasheets, so they are not joined |
| Shapal | 380 to 390 kg/mm2 = 3.7 to 3.8 GPa (Vickers; 2 records) | 2 MPa m1/2 (test method not stated; 1 record) | both properties held, but from different products or datasheets, so they are not joined |
| SiAlON (silicon aluminium oxynitride) | 15 GPa (test not stated; 1 record); 1,600 to 1,800 Knoop (Knoop (number printed with no unit); 1 record) | 7.7 MPa.m 0.5 (method not printed in the table; 1 record) | both properties held, but from different products or datasheets, so they are not joined |
| Yttrium oxide | 6.7 GPa (Vickers; 1 record) | 1 to 4 MPa·m½ (not stated on the page, test method not stated; 2 records) | both properties held, but from different products or datasheets, so they are not joined |
Both held, but the hardness is in a scale we do not convert to GPa 1
Rockwell C and Brinell numbers are not converted to GPa in this article; the pairing would need a conversion table that is not in our data.
| Material | Hardness records as printed | Fracture toughness records as printed | Why it is parked |
|---|---|---|---|
| Stainless steel 440C | 30 to 62 HRC (Rockwell C; 14 records); 223 to 580 HB (Brinell; 2 records) [some at high temperature] | 22 MPa/√m (test method not stated; 1 record) | both properties held, but the hardness is in a scale we do not convert to GPa |
Which ceramic resists chipping best?
Zirconia grades lead the toughness records in our data. Magnesia partially stabilised zirconia (Mg-PSZ), Nilcra Zirconia TS grade prints 15 MPa m^0.5 (per Morgan Advanced Materials). Zirconia as a family spans 5.1 to 15 MPa m^0.5 across datasheets and test methods, so the grade matters more than the family. Silicon nitride follows at up to 6.35 MPa m^0.5.
Fracture toughness measures how well a material resists one crack growing. Chipping of an edge also depends on grain size, surface finish and the load (general engineering knowledge, not in our data), so use the ranking as a guide to which families to shortlist, not as a chip-resistance rating.
| Rank | Material and grade | Fracture toughness, MPa m^0.5 | Test or basis, as recorded | Hardness from the same datasheet | Source |
|---|---|---|---|---|---|
| 1 | Stainless steel 440C | 22 | test method not stated (unit printed as MPa/√m) | none from this datasheet | NASA |
| 2 | Magnesia partially stabilised zirconia (Mg-PSZ), Nilcra Zirconia TS grade | 15 | not printed on the datasheet | 10 GPa (Vickers) | Morgan Advanced Materials |
| 3 | Yttria-stabilised zirconia (YSZ), CoorsTek YTZP | 13 | notched beam, K(Ic) as printed | 12.7 GPa (Knoop) | CoorsTek |
| 4 | Alumina-toughened zirconia (ATZ), ATZ-B | 12.7 | test method not stated | 12 GPa (Vickers) | an ATZ composites paper |
| 5 | Magnesia partially stabilised zirconia (Mg-PSZ), CoorsTek MgO partially stabilised zirconia column | 11 | notched beam, K(Ic) as printed | 11.8 GPa (Knoop) | CoorsTek |
| 6 | Alumina-toughened zirconia (ATZ), ATZ-20 | 10.9 | test method not stated | 13.8 GPa (Vickers) | an ATZ composites paper |
| 7 | Yttria-stabilised zirconia (YSZ), Nilcra Zirconia 3Y-TZP Grade | 10 | not printed on the datasheet | 12.7 GPa (Vickers) | Morgan Advanced Materials |
| 8 | Alumina-toughened zirconia (ATZ), ATZ-10 | 9.8 | test method not stated | 13.1 GPa (Vickers) | an ATZ composites paper |
| 9 | Silicon nitride (Si3N4), NCX-34 | 6.35 | Surface crack in flexure test; unevaluated in the NIST record | none from this datasheet | the NIST Structural Ceramics Database |
| 10 | Magnesia partially stabilised zirconia (Mg-PSZ), Kyocera FZM | 6.3 | DIN EN ISO 23146, SEVNB | 12 GPa (Vickers) | Kyocera |
| 11 | Silicon nitride (Si3N4), SN-GP | 6.2 | Calculated from crack length derived from Vickers hardness indentation, according… | 14.5 GPa (test not stated) | QSil |
| 12 | Titanium diboride (TiB2) | 6.2 | test method not stated | 25 GPa (Vickers) | Munro's 2000 NIST review |
| 13 | Silicon nitride (Si3N4), NBD-200 | 5.5 | test method not stated | none from this datasheet | CoorsTek |
| 14 | Zirconia-toughened alumina (ZTA), CoorsTek Zirconia-Toughened Alumina | 5 to 6 | notched beam, K(Ic) as printed | 14.4 GPa (Knoop) | CoorsTek |
| 15 | Silicon nitride (Si3N4), NBD200 | 5.41 | Surface crack in flexure test; unevaluated in the NIST record | none from this datasheet | the NIST Structural Ceramics Database |
| 16 | Silicon nitride (Si3N4), EC-141 | 5.22 | Surface crack in flexure test; unevaluated in the NIST record | none from this datasheet | the NIST Structural Ceramics Database |
| 17 | Yttria-stabilised zirconia (3Y-TZP), 3Y-TZP reference material from the same paper | 5.1 | test method not stated | 13.8 GPa (Vickers) | an ATZ composites paper |
| 18 | Alumina (Al2O3), CoorsTek AD-995 | 4 to 5 | notched beam | none from this datasheet | CoorsTek |
| 19 | Titanium diboride (TiB2) | 4 to 5 | TiB2 column of the review's property table; test method not stated | 30 GPa (test not stated) | Lv et al.'s 2024 review |
| 20 | Metal boride NbB2 | 4 | dense NbB2 at 97.7 percent of theoretical density; indentation method | 20.3 GPa (test not stated) | Sairam et al. |
| 21 | Silicon carbide (SiC), reaction-bonded SiC | 4 | test method not stated | none from this datasheet | MakeItFrom.com |
| 22 | Boron carbide (B4C), hot pressed boron carbide | 3 to 4 | test method not stated | none from this datasheet | CoorsTek |
| 23 | Molybdenum disilicide (MoSi2), Kanthal Super 1700 | 3 to 4 | test method not stated | 9 GPa (Vickers) | Kanthal |
| 24 | Silicon carbide (SiC), UltraSiC | 3.5 | notched beam, Klc | 26 GPa (Knoop) | CoorsTek |
| 25 | Zirconia-toughened alumina (ZTA), CeramTec Rubalit ZTA | 3.5 | IF method, as printed | none from this datasheet | CeramTec |
| 26 | Aluminium nitride (AlN), AlN-HP | 3.25 | K_IC as labelled in the CoorsTek table; test method not stated | none from this datasheet | CoorsTek |
| 27 | Boron carbide (B4C) | 3.1 | indentation | 27.5 GPa (Knoop) | Saint-Gobain |
| 28 | Aluminium nitride (AlN), AlN 180 | 3.03 | K_IC as labelled in the CoorsTek table; test method not stated | none from this datasheet | CoorsTek |
| 29 | Lanthanum hexaboride (LaB6) | 3.02 | dense LaB6 as stated in the paper; test method not stated in the summary | 20 GPa (test not stated) | Sonber et al. |
| 30 | Silicon carbide (SiC) | 2.78 to 2.82 | Vickers indentation; three loads gave 2.82, 2.81 and 2.78 (NIST) | 23.9 GPa (Vickers) | the NIST Structural Ceramics Database |
| 31 | Aluminium nitride (AlN), typical commercial AlN | 2.6 | test method not stated | 10.8 GPa (test not stated) | Accuratus |
| 32 | Yttrium oxide (Y2O3), Konoshima Y2O3 ceramics | 2.5 | not stated on the page | none from this datasheet | Konoshima |
| 33 | Yttrium oxide (Y2O3), CoorsTek yttria | 1 to 4 | test method not stated | none from this datasheet | CoorsTek |
| 34 | Shapal (AlN-BN), Shapal Hi M Soft | 2 | test method not stated | none from this datasheet | Tokuyama |
| 35 | Silicon nitride (Si3N4), NC-350 | 1.65 | Surface crack in flexure test; unevaluated in the NIST record | none from this datasheet | the NIST Structural Ceramics Database |
What does zirconia give up for its toughness?
Zirconia gives up hardness. The toughest zirconia grade here, Magnesia partially stabilised zirconia (Mg-PSZ), Nilcra Zirconia TS grade, measures 10 GPa and 15 MPa m^0.5 (per Morgan Advanced Materials); the hardest Vickers-tested non-zirconia material, Titanium diboride (TiB2), per Munro's 2000 NIST review, measures 25 GPa and 6.2 MPa m^0.5 (per Munro's 2000 NIST review). The toughest zirconia grade keeps 40% of that hardness and has 2.4 times the toughness.
| Material and grade | Hardness, GPa (test) | Fracture toughness, MPa m^0.5 | Compressive strength, MPa | Hardness against the reference | Toughness against the reference |
|---|---|---|---|---|---|
| Magnesia partially stabilised zirconia (Mg-PSZ), Nilcra Zirconia TS grade | 10 GPa (1,020 kg/mm2 as printed) (Vickers) | 15 MPa m^0.5 | 1,800 MPa | 40% | 2.4x |
| Yttria-stabilised zirconia (YSZ), CoorsTek YTZP | 12.7 GPa (Knoop) | 13 MPa m^0.5 | not found in any source we hold for this grade | not compared (not Vickers) | not compared (not Vickers) |
| Alumina-toughened zirconia (ATZ), ATZ-B | 12 GPa (Vickers) | 12.7 MPa m^0.5 | not found in any source we hold for this grade | 48% | 2x |
| Magnesia partially stabilised zirconia (Mg-PSZ), CoorsTek MgO partially stabilised zirconia column | 11.8 GPa (Knoop) | 11 MPa m^0.5 | 1,750 MPa | not compared (not Vickers) | not compared (not Vickers) |
| Alumina-toughened zirconia (ATZ), ATZ-20 | 13.8 GPa (Vickers) | 10.9 MPa m^0.5 | not found in any source we hold for this grade | 55.2% | 1.8x |
| Yttria-stabilised zirconia (YSZ), Nilcra Zirconia 3Y-TZP Grade | 12.7 GPa (1,300 kg/mm2 as printed) (Vickers) | 10 MPa m^0.5 | not found in any source we hold for this grade | 51% | 1.6x |
| Alumina-toughened zirconia (ATZ), ATZ-10 | 13.1 GPa (Vickers) | 9.8 MPa m^0.5 | not found in any source we hold for this grade | 52.4% | 1.6x |
| Magnesia partially stabilised zirconia (Mg-PSZ), Kyocera FZM | 12 GPa (Vickers) | 6.3 MPa m^0.5 | 2,000 MPa | 48% | 1x |
| Yttria-stabilised zirconia (3Y-TZP), 3Y-TZP reference material from the same paper | 13.8 GPa (Vickers) | 5.1 MPa m^0.5 | not found in any source we hold for this grade | 55.2% | 0.8x |
| Titanium diboride (TiB2), per Munro's 2000 NIST review (reference) | 25 GPa (Vickers) | 6.2 MPa m^0.5 | not found in any source we hold for this grade | 100% | 1x |
One paper in the data, an ATZ composites paper, shows the trade is not fixed: its 3Y-TZP reference sample is 13.8 GPa and 5.1 MPa m^0.5, while its alumina-toughened zirconia samples run 12 to 13.8 GPa and 9.8 to 12.7 MPa m^0.5 (Table 3, unaged samples, Vickers). That is alumina-toughened zirconia (ATZ): a zirconia matrix with alumina added.
On compressive strength, zirconia grades print 1,750 to 2,000 MPa (per the same datasheets as their hardness), while Silicon nitride (Si3N4), SN-GP prints 3,000 MPa (per QSil).
Where does tool steel still win?
On toughness, where a steel has a number. AISI 440C stainless steel prints 22 MPa m^0.5 (per NASA; heat treatment not stated), with 58 to 62 HRC on the same source, 1.5 times the toughest ceramic here. AISI D2 and AISI H13 tool steels hold hardness only (35 to 65 HRC and 45 to 54 HRC) and no toughness.
| Material | Hardness as printed | Fracture toughness, MPa m^0.5 | Can it go on the staircase? |
|---|---|---|---|
| Stainless steel 440C | 58 to 62 HRC (NASA; heat treatment not stated) | 22 (NASA; printed as MPa/√m) | No: the hardness is in HRC |
| AISI D2 cold-work tool steel (EN 1.2379, X153CrMoV12) | 35 to 65 HRC across hardening and tempering conditions | not found in any source we hold | No: HRC, and no toughness |
| AISI H13 hot-work tool steel (EN 1.2344, X40CrMoV5-1) | 45 to 54 HRC across tempering conditions | not found in any source we hold | No: HRC, and no toughness |
| Tungsten carbide (cemented carbide) | 1,200 to 1,605 HV30 (11.8 to 15.7 GPa) | not found in any source we hold | No: no toughness |
A steel is tough in a different way from a ceramic: it usually yields before it fractures (general engineering knowledge, not in our data), which a single KIc number does not capture. The 440C value is a single line from a NASA slide with the heat treatment not stated, and the slide prints its unit as MPa/√m; we read it as MPa m^0.5. Nothing in these numbers says which material to buy: it says which gaps to close before comparing.
Which data on tungsten carbide, zirconia, alumina and silicon carbide is missing?
Not found in any source we hold: a fracture toughness for tungsten carbide, a transverse rupture strength by cobalt grade, a wear rate for any material here, and any hardness or toughness for titanium carbide and niobium carbide. 4 materials hold both values only from different products, so they are not joined. 0 profiles below the quality bar are left out.
- Tungsten carbide toughness. No fracture toughness in any source we hold; only hardness for the cobalt-bonded grades. Transverse rupture strength by cobalt grade is also not found in any source we hold. Compressive strength is held only for pure WC (2.7 GPa, from an aggregator page), not for a cobalt grade.
- One profile for cemented carbide. Tungsten carbide has a single profile, not one per cobalt grade or standard class. 2 cobalt levels are covered (6% and 10%), and the grain size is a printed word, not a measurement.
- Alumina. Alumina's hardness (15.2 GPa Vickers, Kyocera AO479O) and toughness (4 to 5 MPa m^0.5, CoorsTek AD-995) come from different products, so alumina is not on the staircase.
- Wear. No wear-rate record in any covered profile, so nothing here says which material wears slowest. Hardness is a proxy at best (general engineering knowledge, not in our data).
- Scales and tests. Knoop, Vickers and unstated hardness tests are kept apart; Rockwell C, Rockwell A and Brinell hardness are not converted. Toughness methods differ and are listed as recorded.
- Calculated and coating values. 5 calculated hardness records are kept off the plot (chromium carbide (cr3c2) 18.2 GPa, hafnium carbide (hfc) 33 GPa and metal boride wb3 38.3 GPa), as are coating and film hardness values and anything tested above 100 °C.
- No hardness or toughness record. Titanium carbide and niobium carbide.
Questions people ask
Is tungsten carbide harder than ceramics?
Cobalt-bonded tungsten carbide sits in the same hardness range as several ceramics and below the hardest ones. Hyperion Materials prints 1,200 to 1,605 HV30 (11.8 to 15.7 GPa Vickers) across 6 grades. Inside that range: alumina (Al2O3) at 15.2 GPa, alumina-toughened zirconia (ATZ) at 13.8 GPa and yttria-stabilised zirconia (3Y-TZP) at 13.8 GPa. Above it: cubic boron nitride (cBN) at 33 to 45 GPa and titanium diboride (TiB2) at 25 GPa.
What is the fracture toughness of tungsten carbide?
Not found in any source we hold. The Space Mushroom profile for tungsten carbide (cemented carbide) holds hardness for 6 cobalt-bonded grades (1,200 to 1,605 HV30) but no fracture toughness. It records Hyperion Materials tying high toughness to 10 to 20 percent binder, which is a statement about the trend, not a value in MPa m^0.5.
Which has higher fracture toughness, zirconia or alumina?
Zirconia has the higher fracture toughness in every record we hold. Zirconia grades print 5.1 to 15 MPa m^0.5 across 9 records, while alumina prints 4 to 5 MPa m^0.5 for CoorsTek AD-995 (notched beam). The zirconia spread comes from different grades and test methods, so compare datasheets that used the same test.
Is silicon carbide tougher than silicon nitride?
Usually not. Silicon nitride prints 1.65 to 6.35 MPa m^0.5 across 6 records of different forms, and silicon carbide prints 2.78 to 4 MPa m^0.5 across 3. 1 silicon nitride record falls below every silicon carbide record. The gas-pressure-sintered grade SN-GP also prints 14.5 GPa hardness and 3,000 MPa compressive strength (per QSil).
What is the tensile strength of alumina?
Not found in any source we hold. The Space Mushroom profile for alumina holds a flexural (bending) strength of 379 MPa for CoorsTek AD-995 at 20 °C, tested to ASTM F417, which is a different test and is not a tensile strength. Ceramics are usually specified by flexural or compressive strength because they are hard to grip and pull (general engineering knowledge, not in our data).
What does zirconia toughened alumina offer?
Zirconia-toughened alumina (ZTA) is alumina with zirconia particles added to resist crack growth. In our data, CoorsTek ZTA measures 14.4 GPa (Knoop) and 5.5 MPa m^0.5 with 2,900 MPa compressive strength, while CeramTec Rubalit ZTA prints 3.5 MPa m^0.5 (IF method, as printed), with no hardness from that datasheet.
Related on Space Mushroom
- Technical ceramics compared: specific heat, strength, hardness and thermal properties
- Hardness of aluminium, titanium, copper and steel alloys, compared
- Tungsten carbide (cemented carbide): profile, records and sources
- Titanium diboride: profile, records and sources
- Boron carbide: profile, records and sources
- Silicon carbide: profile, records and sources
- Metal borides (transition-metal diborides and boride layers): profile, records and sources
- Lanthanum hexaboride: profile, records and sources
- Silicon nitride: profile, records and sources
- Magnesia-stabilised zirconia and other zirconia grades: profile, records and sources
- Yttria-stabilised zirconia: profile, records and sources
- Aluminium nitride: profile, records and sources
- Molybdenum disilicide: profile, records and sources
- Stainless steel 440C: profile, records and sources
- AISI D2 cold-work tool steel (EN 1.2379, X153CrMoV12): profile, records and sources
- AISI H13 hot-work tool steel (EN 1.2344, X40CrMoV5-1): profile, records and sources
How this was made
Each material is a profile in the Space Mushroom database. The profiles are drafted by AI assistants from the cited pages, and a script checks that every value appears in the source it cites; each profile page lists its sources. Every number on this page is read from those profiles or computed from them in code, and nothing is typed in by hand. A build-time check stops the build if a phrase this page quotes is no longer in its profile.
Pairing rule: a hardness and a toughness are joined only when they come from the same source and the same grade. Units are converted only inside the indentation family (GPa, MPa, MN/m², kgf/mm², HV). The dominated test is the standard Pareto one on the plotted values, using the midpoint of any printed range.
Data checked 2 November 2026. Next review when a profile changes.
How to cite: Space Mushroom, “Tungsten carbide, zirconia, alumina, SiC: hardness against toughness”, https://spacemushroom.com/articles/tungsten-carbide-vs-ceramics-hardness-toughness/, data checked 2 November 2026. Data: CSV of every record used (CC BY 4.0).